There is little information on trauma, posttraumatic stress disorder (PTSD), and associated risk factors in transition-age youth with mental health conditions. This study aimed at understanding the correlates and predictors of PTSD in 84 transition-age youth, between 16 and 21 years old, residing in supported community housing. Chi-square analyses and t tests were used to compare youth with a diagnosis of PTSD to those without a PTSD diagnosis. Stepwise logistic regression analyses were performed to identify unique predictors of PTSD. Of the 84 individuals, 79 (94%) reported a history of trauma, of whom 30 (36%) had PTSD. Sexual abuse was significantly associated with a PTSD diagnosis (r = .47) and the only unique predictor of PTSD (Cox r(2) = .20). Transition-age youth in supported community housing had higher rates of trauma exposure and PTSD than the general adolescent population, suggesting the need for routine assessment and treatment of PTSD in this population.